'84 300SD turbo question?
 

Greetings All,

I have a question about one thing, seeing as this is the first turbo I've owned. I hear this hollow humming sound that starts around 45mph or 1800-1900 rpm and is sometimes present beyond that speed. To me it sounds like either the turbo working or a air leak into the filter housing from a leaking or non-existent filter housing to manifold gasket. The sound isn't a squeal but a dominant droning hum from the engine compartment. The pitch doesn't seem to change with acceleration or deceleration but steady. Does anyone know what I'm talking about? I hope to tear into the air cleaner assembly this Sunday if the weather holds out and see if there is something that is missing like a gasket. Other than what I've just mentioned, the passenger window and drivers rear window don't seem to operate using either the console or door switch. Any ideas on that one would also be greatly appreciated. I do have to say that the PO did review these conditions before viewing this car, and was totally on the up and up as far as what he knew did or didn't work. So far it's been a great car to drive and would definitely be a welcome member to my Benz family. I just need to familiarize myself with turbo engines and this chassis designed car.

Charles

My 300D makes a noise like a timing chain -- sort of a Whirrrrr while the turbo is up -- definitely throttle related.

Lots of possiblities -- a roar type noise could be a leaking exhaust, worse under load, a leak at the EGR (I think mine has one -- black stuff at the base of the diaphram cover), bad connection between turboe and exhaust.

Whines and whistles are high pressure air leaks on the other end of the turbo, or a bad hose between air filter and turbo -- if so, get this one fixed pronto, you are sucking dirt into the engine!

I'm not sure just what kind of noise to expect from an MB turbo -- my Volvo is loud enough to make passengers look for the cop car! My brother's SDL's turbo hasn't worked since he got the car (bad trap oxidizer), and I've not listened to it since the turbo was replace!

The other possibility is a missing exhaust hanger donut, allowing the exhaust pipe to "drum" a certain speeds.

Peter

How are your motor and transmision mounts? I noticed both of my cars became much quieter and smoother after replacing the mounts and they didn't look that bad. They are fairly cheap and it is not too bad of a job. As to your windows, have you tried cleaning the switches they tend to collect a lot of coffe and soda over the years. Also, If your fuses are over five years old just replace them all, they tend to fatigue and fail in ways that can't always be detected with a visual inspection.

Not a Sqeal or Whine sound but a Whoo sound
 

Greetings All,

I'd love to describe this sound better, but if you say whoo loud enough you'll experience the droning hum I am speaking about. It's not driveline related at all and is definitely coming from under the hood at the 1900 rpm range or 45 mph which ever comes first. I did not get a chance to tear into it today, managed to get all glass washed down and dash as well as seats. I want to get the interior looking as nice as it gets and it definitely does look nice. I also played with the moon roof and got the rails all cleaned and relubed. Slides like a sled now. I still have fuel filters to order and change as well as the tranny filter and gasket. Figure if you start with all fresh filters and fluids, you won't have to guess when to do it next.
Looking under the hood without removing any components the EGR valve looks pretty new with no soot on it, as well as the controller valve. I can't imagine them being culprits to this sound. If you have any other ideas of where to look, let me know.

Charles

This is some ride !

Check the turbo to air filter hose for tears. Could be a split vibrating when the turbo comes up. A very dirty air filter will make the turbo sound funny, too -- I can usually tell when I need to change the one on the Volvo.

Speaking of air filters, I'd change yours more often than the recommended milage if you are exposed to much dust -- I live with farms on three sides, and find that I need a new one about every three or four months. When they get visibly dirty I change them. I suppose I could just knock the dust off and put them back in, but they are cheap.

The only bad thing I can think of is if your turbo is shot and is only making a "whooooo" noise instead of making pressure -- my Volvo was VERY quiet -- turned out to be not working. Exceedingly slow acceleration cold! You can check this with a pressure gauge on the boost line (or just disconnect the boost line and see if you loose power badly -- if it drives like with it on, you have no boost!)

Mine makes a yingyinying sound at the same speed, throttle and load related that I assume is the turbo